Micki, there is a chance you could use one of those whole house filters like you asked earlier to use more quantity, but I don't think I would do that. The reason I don't run mine full to the top to bring down PO4 is because I don't want to overdose the tank and I don't want it to clog up and become solid. So using 1", 1.5", or 2" per reactor seems to work just fine. Matter of fact, I'm going to test PO4 in my tank in a few minutes to see what it reads tonight.
Eric, I've used 4-5g of RO/DI water to rinse it out. The reason I used RO/DI instead of tap was due to the idea that any phosphate in the tap water might consume some of the new media. I want all of it to be used in my tank, and not waste it on anything else. The fines are the tiny specs that become waterborne. Depending on what product you'll use, the water will become muddy or cloudy. With Pura Phoslock and Silphos, the water turns blood red. RowaPhos is darker, and Phosban is brownish. You just run water through it slowly to avoid disturbing it too greatly, and stop when the media is visible and the rest of the reactor looks clear.
The only reason I prefer using it in the tank and wasting some tank water is because no air gets in the unit when I'm done purging the unit. When you run it in the sink or in a bucket, once done air gets into the reactor. Then you hook it up to your tank, and start the pump. Water pushes the air down into the reactor, and then burps through the media which sometimes releases more fines. That is a small drawback. It is believed that the fines are detrimental to your system, because it will float through the tank and possibly land on the polyps of your corals.
I've also had the output of the reactor pour into a filter sock to help trap the fines, but I could see dark smoke come right through the sock into the return section. And from there the water goes right back up to the tank.